The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Electron Spectroscopy Studies of Vacuum Deposited Chromium and Cobalt Layers

Jani Sainio

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium L at Helsinki University of Technology (Espoo, Finland) on the 8th of December, 2005, at 13 o'clock.

Overview in PDF format (ISBN 951-22-7880-4)   [1294 KB]
Dissertation is also available in print (ISBN 951-22-7879-0)

Abstract

Vacuum created model systems give the possibility for detailed study of the substrate–adsorbate interaction. In this work two systems have been created by vacuum deposition and these have been characterized with different electron spectroscopies. A chromium oxide model catalyst has been studied with X-ray photoelectron spectroscopy (XPS) and a magnetically interesting epitaxial Co/Cu system has been characterized with low energy electron diffraction (LEED).

Alumina supported chromium oxides are widely used as dehydrogenation catalysts. The nature of the active sites and the reaction paths are still somewhat unclear. We have used the model catalyst approach in order to understand the properties of supported chromium oxide catalysts. The growth of chromium on a thin alumina film has been studied. The oxidation and reduction of this model catalyst and alumina supported chromium oxide catalysts have been compared. The model catalyst can be oxidized under vacuum to the active oxidation state Cr3+, but not further. In calcination and reduction the model catalyst was found to exhibit similar behavior as supported catalyst. This similarity suggests that the model catalyst can be used to study e.g. dehydrogenation reactions carried out on supported chromium oxides despite of the structural differences.

The chemical state information obtained from XPS measurements by peak fitting is subject to many systematic and random errors. We have studied the effect of the background subtraction method on the derived chemical state proportions of chromium and iron oxides with two oxidation states. The effect of the background choice was found to be comparable to typical systematic errors related to uncertain peak fitting parameters.

Epitaxial layers of Co and Cu show interesting magnetic properties, such as giant magnetoresistance. Undesired interface mixing has been observed when growing these layers. In this work Co was deposited onto a Cu(001) single crystal to model the interface structure. Co was found to form random surface alloys exhibiting substitutional copper sites. When the Co coverage increases to several monolayers, a transition to layer growth is observed. These findings can be used to model the magnetic properties of Co/Cu layers.

This thesis consists of an overview and of the following 6 publications:

  1. M. Eriksson, J. Sainio, and J. Lahtinen, Chromium deposition on ordered alumina films: an x-ray photoelectron spectroscopy study of the interaction with oxygen, Journal of Chemical Physics 116, 3870-3874 (2002). © 2002 American Institute of Physics. By permission.
  2. J. Sainio, M. Eriksson, and J. Lahtinen, Interaction of oxygen with chromium deposited on Al2O3/NiAl(110), Surface Science 532-535, 396-401 (2003). © 2003 Elsevier Science. By permission.
  3. S. Airaksinen, O. Krause, J. Sainio, J. Lahtinen, K.-j. Chao, O. Guerrero-Pérez, and M. Bañares, Reduction of chromia/alumina catalyst monitored by DRIFTS-mass spectrometry and TPR-Raman spectroscopy, Physical Chemistry Chemical Physics 5, 4371-4377 (2003).
  4. J. Sainio, M. Aronniemi, O. Pakarinen, K. Kauraala, S. Airaksinen, O. Krause, and J. Lahtinen, An XPS study of CrOx on a thin alumina film and in alumina supported catalysts, Applied Surface Science 252, 1076-1083 (2005). © 2005 Elsevier Science. By permission.
  5. M. Aronniemi, J. Sainio, and J. Lahtinen, Chemical state quantification of iron and chromium oxides using XPS: the effect of the background subtraction method, Surface Science 578, 108-123 (2005). © 2005 Elsevier Science. By permission.
  6. J. Sainio, E. AlShamaileh, J. Lahtinen, and C. Barnes, Initial growth of Co on Cu(001) studied with LEED I(V), Surface Review and Letters 10, 641-648 (2003). © 2003 World Scientific Publishing Company. By permission.

Keywords: model catalyst, chromium oxide, cobalt, photoelectron spectroscopy, low energy electron diffraction

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© 2005 Helsinki University of Technology

Last update 2011-05-26